Toughened and Corrosion- and Wear-Resistant Composite Structures and Fabrication Methods Thereof

ABSTRACT

Composite structures having a reinforced material interjoined with a substrate, wherein the reinforced material comprises a compound selected from the group consisting of titanium monoboride, titanium diboride, and combinations thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending U.S. patent applicationSer. No. 12/122,024, filed May 16, 2008, entitled “Toughened andCorrosion- and Wear-Resistant Composite Structures and FabricationMethods Thereof,” the entire contents of which are incorporated byreference herein.

GOVERNMENT RIGHTS

The U.S. Government has rights to this invention pursuant to contractnumber DE-AC05-00OR22800 between the U.S. Department of Energy andBabcock & Wilcox Technical Services Y-12, LLC.

FIELD

This disclosure relates to the field of coatings and surface treatmentsfor metals. More particularly, this disclosure relates to the formationof reinforced titanium and boron materials interjoined with substratesto provide a composite structure.

BACKGROUND

Titanium alloys, aluminum alloys, and steels have physical and chemicalproperties that are often desirable for a wide variety of staticstructural applications. However, these alloys often do not provide thewear and corrosion resistance that is required in many rotating orreciprocating machine applications such as in aircraft propeller blades,compressor turbine blades, bearings, pistons, and similar wear parts anddynamic machinery components. For example, titanium alloys haveattractive properties such as high specific strength and stiffness,relatively low density, and excellent corrosion resistance, but titaniumalloys typically have poor resistance to wear and oxidation at hightemperatures. Aluminum castings are light in weight but provide littleresistance to galling and other wear-related phenomena even at moderatetemperatures. Steels have high strength and may be surface hardened bysuch techniques as nitriding and carbiding, but still the wearresistance of such surface-hardened steel alloys is inadequate for manyapplications.

Techniques such as plasma spraying, sputtering, and plating have beendeveloped to add a wear resistance layer to the surface of metalsubstrates. However these techniques often result in distortion ofsubstrate geometry, reduction of surface smoothness, and eventualdelamination of the added layer from the substrate. Therefore bettermaterials and techniques are needed for improving the corrosion and wearresistance of the surfaces of metals.

SUMMARY

In one embodiment the present disclosure provides a method of making acomposite structure that includes a step of disposing a precursormaterial comprising titanium diboride on at least a portion of asubstrate. The method further includes the step of heating the precursormaterial and the at least a portion of the substrate in the presence ofan oxidation preventative until at least a portion of the precursormaterial forms a reinforced material that is interjoined with the atleast a portion of a substrate to provide the composite structure.

A further embodiment of making a composite structure includes a step ofdisposing a precursor material comprising boron on at least a portion ofa substrate; and a step of heating the precursor material and the atleast a portion of the substrate in the presence of available titaniumand an oxidation preventative until at least a portion of the precursormaterial forms a reinforced material that is interjoined with the atleast a portion of the substrate to provide the composite structure.

Also provided is a composite structure that has a reinforced materialinterjoined with a substrate. The reinforced material includes acompound selected from the group consisting of titanium monoboride,titanium diboride, and a combination thereof.

A welding rod embodiment is provided. The welding rod includes a metalelectrode and a precursor material is disposed adjacent at least aportion of the metal electrode. The precursor material includes amaterial selected from the group consisting of: titanium diboride,titanium monoboride, and a combination thereof.

A material for use in forming a composite structure is provided. Thematerial typically includes a precursor material that includes a fluxand a material selected from the group consisting of: titanium diboride,titanium monoboride, and a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Various advantages are apparent by reference to the detailed descriptionin conjunction with the figures, wherein elements are not to scale so asto more clearly show the details, wherein like reference numbersindicate like elements throughout the several views, and wherein:

FIG. 1 is a photomicrograph of an as-reacted TiB composite materialmorphology on a Ti substrate.

FIG. 2 is a photomicrograph of TiB needles on a Ti substrate.

FIG. 3 is a photomicrograph of a Ti metal matrix with TiB needles andpillars disposed on a Ti substrate.

FIG. 4 is a photomicrograph of TiB needles disposed on a Ti substrate.

FIG. 5 is a Ti-B phase diagram.

FIGS. 6A-6C are somewhat schematic cross-sections of welding rods.

FIGS. 7A and 7B are somewhat schematic perspective views of grinders.

FIG. 8A is a schematic layout of reinforced materials interjoined with aTi substrate.

FIG. 8B is a schematic layout of reinforced materials interjoined with amild steel substrate.

FIG. 8C is a schematic layout of reinforced materials interjoined with aTi substrate.

FIG. 9 is a photomicrograph of a cross section of a Ti substrate.

FIGS. 10-16 are photomicrographs of cross-sections of reinforcedmaterials interjoined with a Ti substrate.

FIGS. 17 and 18 are plots of hardness values at measured depths near thesurfaces of the structures of FIGS. 9-16.

FIGS. 19-22 are photomicrographs of reinforced materials interjoinedwith a mild steel substrate.

FIGS. 23 and 24 are plots of hardness values at measured depths near thesurfaces of the structures of FIGS. 19-22.

FIGS. 25-27 are photomicrographs of reinforced materials interjoinedwith a Ti substrate.

FIG. 28 is a plot of hardness values at measured depths near thesurfaces of the structures of FIGS. 25-27.

DETAILED DESCRIPTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings, which form a parthereof, and within which are shown by way of illustration the practiceof various embodiments of reinforced material structures that areinterjoined with suitable substrates to form composite structures, andmethods for forming such reinforced materials and creating compositestructures. It is to be understood that other embodiments may beutilized, and that structural changes may be made and processes may varyin other embodiments.

Various embodiments described herein provide methods for forming areinforced material that is interjoined with a substrate. A reinforcedmaterial may be formed over the entire surface or over only a portion ofthe surface of a substrate. Substrate materials may include elementalmetals or metal alloys such as titanium or titanium alloys, or aluminumor iron or aluminum or ferrous or other non-titanium metals or alloys,or ceramics, polymers, composites, and combinations thereof. In someembodiments the substrate is titanium. In some embodiments the substrateis a titanium alloy. In some embodiments the substrate is an aluminumalloy. In some embodiments the substrate is a ferrous alloy or steel.

The process of forming a reinforced material interjoined with asubstrate typically involves disposing a precursor material on thesubstrate and then heating the precursor material and heating at least aportion of the substrate until at least a portion of the precursormaterial forms a reinforced material interjoined with the substrate. Theresult is a “composite structure.” The composite structure is thecombination of the reinforced material and the substrate and the regionswhere they are interjoined. In some cases the substrate and thereinforced material may entirely intermingle, in which case thereinforced material and the substrate are still considered to beinterjoined, and the composite structure is the intermingled materials.

A precursor material may include a single ingredient such as titaniumdiboride, or a precursor material may include multiple ingredients suchas boron and titanium. When reference is made to a precursor materialcomprising a chemical element such as boron or titanium, it is meant theprecursor material includes the chemical element as elemental material(e.g., titanium metal or boron metal), or as a compound of the metal, oras an alloy (such as the Ti-6-4 alloy), or an inter-metallic (such asTiAl), or as a mixture or blend of the metal, or as a combination ofthese forms.

The process of interjoining typically involves heating the precursormaterial and heating at least a portion of the substrate to provide thecomposite structure. As a result of the process one or more of thefollowing effects may occur to form a composite structure: at least aportion of the precursor material may diffuse into the substrate, aportion of the substrate may diffuse into the precursor material, atleast a portion of the precursor material may be bonded to thesubstrate, at least a portion of the precursor material may alloy withthe substrate, and/or at least a portion of the precursor material andat least a portion of the substrate may form a mixture.

After processing, the reinforced material that is interjoined with thesubstrate may have substantially the characteristics of a coating on thesurface of the substrate, or the reinforced material may havesubstantially the characteristics of a modification of the surface ofthe substrate. The nature of the reinforced material that results from aprocess for applying a reinforced material to the substrate, i.e.,whether the process results in a coating or in a surface modification,depends upon the substrate material, the deposited material, and thespecific processing parameters that are used to form the reinforcedmaterial. In the cases where the end result is a coating, at least aportion of the deposited material adheres to the surface of thesubstrate. In the case of surface modification, a portion of thedeposited material is intermingled with a portion of the material at thesurface of a substrate where a reinforced material is formed. Theresultant modification of the surface may include the formation of analloy or a new combination of materials at or below the original surfaceof the substrate.

Typically the formation of reinforced materials as disclosed hereininvolves various material microstructure modifying mechanisms, includingsintering, alloying and precipitation. Sintering refers to densificationand chemical bonding of adjacent particles which is affected by heatingto a temperature near (and preferably below) the melting point of boththe substrate and precursor material. Sintering may occur at theinterface between the coating and the underlying substrate surface toimprove interfacial adhesion. In addition, sintering may occur withinthe coating material itself, to improve densification and mechanicalstrength of the coating material. The term alloying refers to heatingthe substrate and coating materials above their respective meltingpoints to produce an interface comprising a mixture of the substrate andcoating materials. Alloying is a desirable mechanism for producingimproved adhesion between the coating and a portion of the underlyingsubstrate. The term precipitation describes a material modificationprocess whereby the material being modified, i.e., the depositedmaterial and/or the substrate surface, is heated to produce a new solidphase which gradually precipitates within the particular solid alloymaterial as a result of slow, subsurface chemical reaction. This type ofreaction is generally used to harden a substrate surface.

In some embodiments the precursor material is provided in powder form.In some embodiments the powder may be mixed with a liquid suspensionmedium, or carrier, to form a slurry. The term slurry is used todescribe a precursor material having a watery consistency and comprisinginsoluble matter in a liquid. The carrier acts as a medium for carryingor transporting the coating materials to the substrate surface. Forexample, the liquid carrier may consist of water, alcohol, awater-alcohol mixture, an alcohol-ethylacetoacetate mixture, or analcohol-acetone mixture, to name just a few. The carrier is typicallyevaporated when the precursor material is heated to form the reinforcedmaterial. There are a number of commercially-available suspension mediathat may be used. For example, experiments were performed using HPC, thecommercial designation of a carrier medium manufactured by ZYP Coatings,Inc. of Oak Ridge, Tenn. This particular suspension medium consists ofapproximately 98% water and approximately 2% Mg—Al-silicate.

The slurry may comprise additional components for controlling physicalcharacteristics of the slurry. For example, surface active agents, orsurfactants, such as sodium lauryl sulfate, polyvinyl alcohol andwater-soluble linear polyethylene glycols (PEGs) available from DowChemical Co. of Midland, Mich. under the tradename CARBOWAX, may beadded to maintain suspension of the solid phase. Lubricants, such asstearic acid, may be added to assist in consolidation of the slurrycomponents.

In some embodiments a precursor material may be formed with a binder,such as an organic or plastic material, a solder or a brazing alloy, orsimilar material. The binder is a material that acts as an adhesive tohold the precursor material together. In some embodiments the precursormaterial and the binder may be formed as a sheet or a tape and in someembodiments the precursor material and the binder may be formed as apaste. In many embodiments the binder has a low melting temperature,meaning that the binder has a melting point below the melting point ofthe other components of the precursor material or the melting point ofthe substrate. Upon melting, the binder wets to the substrate surfaceand wets/embodies the coating powder particles. In some instances, thebinder material, like the carrier in a slurry, is evaporated orpyrolized when the precursor material is heated to form the reinforcedmaterial. In other instances, all or a portion of the binder may remainin the formed reinforced material, acting as a part of the matrixmaterial.

Typically, a powder, slurry, or paste that is the precursor material isdisposed on a substrate by brushing, rollering, spray-drying, orspray-painting. However, one skilled in the art will recognize thatalternate deposition methods may also be used. For example, the surfaceto be protected may be immersed in the mixture or a slurry may bespray-dried upon the substrate. Another example of a precursor materialdeposition process is thermal spraying. Thermal spraying is adaptable tothe deposition of ceramics, metals and metal alloys, polymers,composites, ceramic-metals and multi-component, graded, or multilayeredcombinations of these materials.

When the precursor material is a slurry or a paste, it is referred toherein as a “glaze.” The glaze may be allowed to dry or cure (or may beforced to dry or cure by heating it to a temperature that is typicallybetween 500° C. and 1000° C.) before heating the glaze to form thereinforced material interjoined with the substrate to form a compositestructure. Temperatures lower than 500° C. may be used to dry or curethe glaze in embodiments where a low boiling point carrier like alcoholis used to form the glaze.

Typically, the reinforced material is reactively formed by heating thedeposited material and the substrate surface by using laser, plasma,infrared, electron beam, gas torch, or electric arc (e.g., tungsteninert gas [TIG]) heating sources. Such heating techniques that heat onlya local area of a substrate are referred to as “localized surfaceheating techniques.” In contrast, “bulk material heating techniques”refer to techniques that heat an entire substrate such as gas, electric,or microwave ovens, or induction or other types of furnaces.

Formation of a reinforced material on a substrate is preferablyaccomplished by heat-treating the precursor material using a high heatflux process such as infrared (IR) radiation. In contrast to many otherheating techniques, IR radiation heating provides a means for rapidlyheating the deposited material while maintaining a substantially lowersubstrate temperature. Infrared radiation heating is preferablyperformed in an IR heating furnace. A variety of IR sources areavailable. For instance, tungsten-halogen based IR sources or a morepowerful IR furnace, incorporating a plasma-based IR source, areavailable. The plasma-based IR furnace typically operates as aline-focus type system, where the precursor materials are heated by anIR beam as it scans across the substrate.

Preferably the formation of the reinforced material is accomplished byfirst heating, for up to a few seconds, the precursor material and thesubstrate to a temperature above the α-to-β phase transformationtemperature (e.g., approximately 884° C. for TiB coating materials) butbelow the eutectic temperature (e.g., approximately 1540° C. for TiBcoating materials). Then preferably the precursor material and thesurface of the substrate are heated, for up to a few seconds, to atemperature slightly above the melting temperature of the substrate. Bymaintaining the bulk temperature of the substrate below its meltingtemperature, the reinforced material is formed while maintaining much ofthe microstructure of the underlying substrate material.

The temperature to which the precursor material and the substrate areheated may be accurately controlled by varying the intensity of IRradiation and the time of exposure to the IR radiation source. Theintensity of IR radiation and time of exposure to IR radiation willgenerally vary depending on characteristics of the substrate anddeposited materials, and the coating or surface modification that isdesired. For most applications, the IR exposure time ranges from 1 to300 seconds, with an exposure time of 30 to 60 seconds being preferred.The preferred IR intensity, or heat flux density, will generally rangeup to a maximum value of about 3,500 Watts/cm². However, these variablesare application-specific and deviations therefrom may be employed. Thetime of exposure to heat (as by IR radiation) may be varied to controlthe extent of base metal dissolution into the coating, therebycontrolling the thickness and final composition of the coating. Forinstance, particular applications may incorporate non-uniform and/ornon-continuous heating profiles to produce coating thickness variationsor coating composition gradient structures.

Infrared heating rapidly increases coating density by eliminating poresformed in the coating during deposition. IR heating also typicallyimproves the cohesiveness of the coating material and/or the adhesion ofthe coating material to the substrate surface. It may be desirable toseparately heat a portion of the substrate surface in addition toheating the deposited material, such that the microstructure of theheated portion of the substrate surface is altered. The degree to whichthe substrate surface microstructure is altered depends on a number offactors, including the materials from which the substrate is formed anddeposited materials that are used, duration of heating, and themicrostructural properties desired.

Infrared heating is beneficial in that it may be applied to a variety ofcomplex surface contours generally without requiring significantcustomization of the heating system configuration. Many alternative highheat flux methods require a physical coupling of the heat source to thecoated surface, such as with an induction coil. A typical induction coilmay not couple uniformly to the entire surface when the substratesurface geometry is complex. Therefore, avoiding non-uniform heating ofthe coating surface requires specially designing a coil that follows thecontours of the particular substrate. Such customization is generallynot required with IR heating. Although the specific intensity of thethermal energy may be expected to decrease as a function of distancebetween the IR source and the coating surface due to dispersion of theradiation, this decrease in energy is typically insignificant.Consequently, with IR heating a substrate coating may often be uniformlyheated without any special effort to customize the heat source toaccommodate the substrate's surface geometry. IR heating provides thefurther advantage of enabling the flexibility to heat (and therebymodify) selected portions of a surface. This is possible since the IRradiation may be directed or focused toward a particular surface area.

Turning now to more particular aspects of various embodiments, thematerial that is deposited on a substrate typically consists of titaniumor a titanium alloy powder, and boron or a boron containing material. Inpreferred embodiments the deposited material includes titanium metal andtitanium diboride. The titanium metal acts as a source to feed theformation of TiB and TiB₂ and any residual titanium provides furthercorrosion resistance and hard second phase materials. A fluxing agentsuch as CaF₂ may be added to the precursor material in order to reduceoxidation of the substrate metal. Fluxing agents are materials that areused to prevent oxidation during heating operations, but that may besubstantially entirely removed after heating the precursor material andthat do not contribute any significant bonding, hardening, or wearresistance functionality to the reinforced material. The utility of afluxing agent and the utility of a binder may be provided by a singlematerial.

Si or B may be added as a self-fluxing material. The term self-fluxingmaterial refers to a material that forms part of the reinforcedmaterial, and that contains elements for removing oxides (such as bydissolution or chemical reduction) and that facilitates wetting of thesubstrate. That is, self-fluxing materials “wet” the substrate andcoalesce when heated to their melting point without the addition of afluxing agent. Si or B act as self-fluxing materials in part becausethey tend to form eutectics with the other materials, which lower thereaction temperatures and reduce the oxidation rate. Boric acid (H₃BO₃)typically acts as a fluxing agent, but it may act as a self-fluxingmaterial where the boron forms part of the reinforced material.

The term “flux” is used herein to refer to either a self-fluxingmaterial or a fluxing agent, or a combination of a self-fluxing materialand a fluxing agent. The absence of a flux generally hinders wetting ofthe substrate. Generally, precursor materials containing self-fluxingmaterials that are deposited on a substrate may be heated in regularopen atmosphere without oxidation of the substrate. Materials notcontaining self-fluxing materials that are deposited on a substrate as aprecursor material typically must be either (a) supplemented with afluxing agent or (b) heated in a protective atmosphere during formationof the reinforced material in order to prevent oxidation of thesubstrate and/or the precursor materials. The protective atmosphere maybe an evacuated environment, an inert gas environment, or a reducing gasenvironment. For example, an argon-hydrogen (4% H₂) atmosphere workswell. The term “oxidation preventative” is used herein to refer toeither (1) a protective atmosphere or (2) a fluxing agent or (3) aself-fluxing material, or (4) to a combination of two of the previousthree or a combination of all of the previous three.

The formation of β-titanium is preferred in the reinforced material. Aβ-titanium stabilizer such as Mo and Nb powders (either dry or in liquidsuspension) may be added to the precursor material in order to promotethe formation of β-titanium.

Typically the precursor material is heated until the precursor materialmelts. Generally the heating is done in an inert atmosphere to minimizeoxidation of the metallic substrate and/or the precursor material. Atemperature above 1000° C. is typically required and preferably thesurface of the metallic substrate being treated is at a temperature nearthe melting temperature of the substrate. As used herein the term “nearthe melting temperature of the substrate” means a temperature betweenapproximately 60% and approximately 150% of the melting temperature ofthe substrate. Various techniques may be used to prevent the melting ofthe bulk of the substrate even though the temperature at the surface ofa substrate exceeds its melting temperature. For example, the surfacemay be heated for a period of time that is short enough to preventenough heat conduction into the body of the substrate to melt thesubstrate. Typically the result is that a thin reinforced material oftitanium, titanium boride, and titanium diboride is interjoined with thesubstrate. Preferably the reinforced material is predominantly titaniummonoboride in the presence of titanium, and the reinforced materialpreferably includes β-Ti. The reinforced material may also includetitanium diboride, borides of chromium, tantalum, iron, nickel, andother metal alloys, and, in some cases, carbides of these metals. When afluxing agent or a self-fluxing material is used and the flux forms slagcrusts after the reactive heating or melting, little or no slagtypically remains in the resultant reinforced material.

The composite structures formed by these techniques result in a changeto at least the surface characteristics of a substrate, typically toprovide a composite structure having properties of high hardness, hightemperature strength, and wear and corrosion resistance. These changesmay be made adjacent the surface of the substrate without changing thebulk material properties (e.g., density, modulus of elasticity, yieldstrength) of the substrate. In some composite structure embodimentsdiscernible layers of reinforced materials are formed interjoined withthe substrate. In some embodiments functionally graded reinforcedmaterials may be interjoined with the substrate, a configuration thattends to increase bonding strength and adherence and mitigatedifferences in coefficient of thermal expansion (CTE). In someembodiments the process of forming the reinforced material modifies thesubstrate from its surface to a depth under the surface of approximatelyfive microns or less. In some embodiments the process of forming thereinforced material modifies the substrate from its surface to a depthof approximately ten centimeters or so. In some embodiments the processof forming the reinforced material modifies the entire bulk of thesubstrate and the resulting composite structure contains no significantamount of unmodified substrate material. The reinforced materials may befabricated on finished components by portable, field techniques or maybe fabricated on bulk (e.g., sheet) materials prior to finalmanufacturing steps.

In preferred embodiments high aspect ratio particles of TiB are formedas part of the reinforced material. “High aspect ratio” particles refersto particles with three-dimensional morphologies wherein one dimensionof a particle is approximately at least five times longer than either ofthe other two dimensions of the particle. The high-aspect ratiomorphology is preferred because it provides improvements in stiffness,strength, creep resistance, and hardness of the reinforced material.

FIGS. 1-4 present photomicrographs illustrating the results of disposingand interjoining either TiB₂ on a Ti substrate or B+Ti on a Ti substrateto form a reinforced material that is interjoined with the substrate.These and other precursor material formulations may include a flux suchas boric acid. When TiB₂ is used as a precursor material on a Tisubstrate a reaction that may occur in the process of forming areinforced material is TiB₂+Ti→2TiB. When B is used as precursor with aTi substrate, the reaction product (reinforced material) ispredominantly also TiB because of the presence of titanium from thesubstrate.

On non-titanium substrates a source of titanium and boron is needed inthe precursor material in order to form TiB₂ or TiB as reinforcedmaterial. It should be noted that in any reaction between Ti and B, TiBis formed first (rather than TiB₂), but if enough time and heat isprovided for the reaction to go to equilibrium, TiB₂ will be thedominant compound produced, unless excess titanium is available. “Excesstitanium” is titanium that is present in sufficient stoichiometricquantity to convert into titanium monoboride (TiB) substantially anytitanium diboride (TiB₂) that is either present in the precursormaterial or that forms during the reaction process. According to thephase diagram of FIG. 5, TiB has boron at an atomic percent of 50% and aweight percent of 18.4% whereas TiB₂ has boron at an atomic percent of66.7% and a weight percent of 31.1%. Therefore, for example, if the B:Tiatomic ratio is 1:1 (meaning that the atomic % ratio between B and Ti is50:50 atomic %), then substantially only TiB is formed. That is, for TiBformation the mole ratio is 1:1 (e.g., 47.90 grams [or 1 mole] of Ti(81.6 wt. %) to 10.81 grams [or 1 mole] of B (18.4 wt. %). If the B:Tiatomic ratio is 2:1 (meaning that the B:Ti atomic % ratio is 66.7:33.3atomic %) then substantially only TiB₂ is formed. That is, for TiB₂formation the mole ratio is 2 moles of B to every 1 mole of Ti (e.g.,47.90 grams [or 1 mole] of Ti (68.9 wt. %) to 21.62 grams [or 2 moles]of B (31.1 wt. %).

Titanium that is present to react with boron and produce TiB and/or TiB₂but is not present in sufficient stoichiometric quantity to convertsubstantially all TiB₂ to TiB at equilibrium is referred to herein as“available titanium.” Available titanium and excess titanium may beprovided by titanium that is present in the substrate or may be providedby a source of titanium that is included as a precursor materialdisposed on the substrate as part of the process to form the reinforcedmaterial. Examples of a source of titanium that may be included in aprecursor material disposed on the substrate include titanium metal,titanium alloys such as the Ti-6-4 alloy, Ti inter-metallics such asTiAl, Ti blends, and other titanium compounds, especially those thathave thermodynamically favored reactions with TiB₂. The formation ofreinforced materials interjoined with a substrate may occur in thepresence of available titanium or in the presence of excess titanium.

FIG. 1 illustrates an as-reacted TiB coating morphology on a Tisubstrate. Eutectic TiB needles 10 are depicted along with primary TiBpillars 20. The pillars 20 have an aspect ratio (length/width) ofbetween one and five and the needles 10 typically have an aspect ratioof greater than five. Sometimes the needles have an aspect ratio greaterthan ten. Titanium metal 30 also forms part of this multi-phasemicrostructure coating on a Ti substrate 40. FIG. 2 illustrates TiBneedles 10 along with titanium metal 30 formed as a coating on a Tisubstrate 42. FIG. 3 illustrates a Ti metal matrix 40 disposed on a Tisubstrate 44. FIG. 4 illustrates TiB needles 10 disposed on a Tisubstrate 46.

Some examples of formulations of precursor materials that may be usedfor formation of reinforced materials are shown in Table 1.

TABLE 1 For- Composition of Precursor Material mula- (Parts by Weight)tion Boric Surface Layer No. TiB₂ CrB Acid B Ti-6-4 Reaction Components1 25 2.5 2.5 0 0 TiB₂ + Ti → TiB, Ti, & CrB 2TiB on Ti-6-4 2 25 5 2.5 00 TiB₂ + Ti → TiB, Ti, & CrB 2TiB on Ti-6-4 3 25 2.5 5 0 0 TiB₂ + Ti →TiB, Ti, & CrB 2TiB on Ti-6-4 4 25 0 2.5 0 0 TiB₂ + Ti → TiB & Ti on2TiB Ti-6-4 5 0 0 2.5 15 25 2Ti + 3B → TiB & Ti on TiB + TiB₂ Ti-6-4 6 025 2.5 0 25 [None] CrB on Ti-6-4 Note that titanium metal, Ti-6-4powder, or other titanium alloys could be added to any of formulationNos. 1 through 4.

As illustrated in FIGS. 1-4, during the melting of the precursormaterial, pillar-shaped primary TiB structures (pillars 20) or fineneedle-shaped eutectic TiB structures (needles 10) may be formed in themelted region, depending upon the boron content. FIG. 5 presents anequilibrium Ti—B phase diagram. FIG. 5 generally illustratescharacteristics of processes and materials described herein, but becauseof rapid heating and cooling and abrupt changes in materialconcentration gradients, the compositions and reactions disclosed hereingenerally represent non-equilibrium conditions that do not preciselyconform to FIG. 5. The melting temperature of titanium is approximately1668° C. and the melting temperature of boron is approximately 2076° C.A precursor material of approximately 98.3 wt. % titanium andapproximately 1.7 wt. % boron forms a eutectic reaction which melts theprecursor material at approximately 1540° C. When the boronconcentration exceeds the eutectic concentration (1.7 wt. %),pillar-shaped (primary) TiB forms first until the concentration of borondecreases to approximately 1.7 wt. %, and then needle-shaped (eutectic)TiB is formed. Substantially only eutectic TiB is formed when the boronconcentration value is equal to or below 1.7 wt. %. The pillar-shapedprimary TiB is typically hexagonal in cross-section.

The solubility of boron in titanium is nearly zero, and, thus, the TiBphases are substantially only formed during solidification. A hardsurface phase separates out in the form of thin ramified crystals thatact as micro-reinforcement of a metallic matrix surface. The resultingstructures provide an alloy with higher abrasive wear resistance thanthat provided by primary phase structures. TiB may also improvehigh-temperature properties, since TiB is insoluble and chemicallystable at temperatures over 1000° C.

TiB is a very compatible coating for titanium substrates. TiB has ahigher elastic modulus value (371 GPa) than most titanium alloys(100-120 GPa), a coefficient of thermal expansion close to Ti(6.2×10⁻⁶/° C. for TiB and 8.2 10⁻⁶/° C. for Ti), and a density of 4.56g/cc compared to 4.5 g/cc for Ti. A powder blend or slurry containingMoB powder, TiB₂ powder, and CaF₂ flux may be applied to Ti alloysubstrates such as Ti-6Al-4V. Mo and Nb powder may be added asβ-stabilizing elements. With a powder blend or slurry having a fluxmixing ratio of 40 wt. % flux, the melted region typically forms a 1.1.to 1.5 mm thick reacted surface of TiB that is substantially interjoinedwith the substrate without significant defects. The formation of the TiBin the melted region typically greatly improves the Vickers hardness,high-temperature Vickers hardness, and the wear resistance to levelsthat may be 2 to 5 times higher than those of the Ti alloy substrate.

The addition of MoB powders to a precursor material allows thefabrication of surface-alloyed materials with various properties bycontrolling the kind, size, and volume fraction of TiB in the surfacematrix. For example, on Ti alloy substrates, the melted region formed byprecursor powder blends containing TiB₂ and 40 wt % CaF₂ flux orTiB₂-MoB-40 CaF₂ have contained hexagonal-pillar-shaped primary boridesand needle-shaped eutectic borides, whereas only needle-shaped eutecticborides have been found when MoB-40 CaF₂ blends were used. This isdirectly related to the amount of boron in the melted region. TheTiB₂-40CaF₂ blend provided the highest hardness and wear resistance. Thewear resistance improves as the TiB volume fraction or hardness in themelted region increases. When MoB is added to the blend, Mo dissolves inthe Ti matrix and promotes β-Ti transformation since Mo is a β-Tistabilizer. Since β-Ti is harder than α-Ti, the presence of Mo affectsthe overall hardness. Additionally, Mo. provides a smoother surfaceimportant to many wear applications. Titanium has a higher chemicalaffinity for boron atoms than molybdenum; therefore, TiB forms insteadof MoB.

The proper amount of flux prevents oxide formation by protecting thepowder melt from air, by decomposing TiO₂, and by precipitating boridesevenly in the melted region by homogenous melting boride powders. A fluxmay be specifically selected so that no chemical reaction occurs betweenthe flux and the substrate, and therefore the flux does not affect thecomposition of the resulting reinforced material. For example, CaF₂ fluxreacts with TiO₂ and H₂O to from CaO which forms as a slag on thesurface and prevents oxidation of the melted region by protecting themelted region from the air. The slag does not form part of thereinforced material. Generally it is desirable to use the smallestamount of flux possible to increase the volume fraction of boride andhardness. The resultant surface is typically a uniform, continuous, andcrack-free coating with a sound and adherent interface with the metalalloy substrate, such as titanium or steel for examples.

As previously indicated, TiB also plays a role in improvinghigh-temperature properties of a reinforced material, since TiB isinsoluble and chemically stable at temperatures over 1000° C. Theformation of TiB₂ on the surface of a substrate also provides a usefulcomposite structure. Titanium diboride (TiB₂) is a ceramic having asemi-metallic nature. A metallic matrix (composite structure) formed ofsteel and titanium diboride has an abrasive wear resistance that isseveral times greater then the abrasive wear resistance of steel. Theinclusion of TiC is also useful in reinforced materials for steel andother substrates. A precursor powder blend containing TiB₂ and TiC witha flux may be sintered at approximately 1232° C. to form a hard-facedcoating on metallic substrates. The 1232° C. is lower than the meltingtemperature of titanium (1668° C.) so that application of the coating at1232° C. typically does not melt a titanium substrate. In the case oftitanium substrates, the TiC is stable with sufficient diffusion at theparticle-titanium interface to create good bond strength. The TiB₂particles react with the Ti substrate in-situ, transforming theparticulate TiB₂ to TiB needles, which further improves the utility ofthe reinforced material. TiB₂ has a hexagonal phase with an “AlB₂structure.” In an AlB₂ structure, the so-called “X” atoms (Boron) areclosely packed in a hexagonal arrangement and the so-called “A” atoms(Ti in the case of TiB₂ or Al in the case of AlB₂) occupy the triagonalprismatic interstices. The TiB formed by the reaction of Ti and TiB₂occurs predominantly as needles embedded in excess Ti and typically theTiB is of an FeB type structure containing boron chains.

In further embodiments, high wear and corrosion resistant surfaces maybe formed on metal alloy substrates as surface alloying or reactivesurface modifications by depositing and heating combinations ofmaterials selected from boron, titanium diboride, molybdenum boride,silicon, self-fluxing materials, titanium, chromium boride, chromium,nickel, iron, molybdenum, niobium, and carbides.

Additional examples of precursor materials include self-fluxingmaterials deposited on substrates by thermal spray, slurry spray,painting, etc., and subsequently interjoined using a heating process(infrared, laser, electron beam, etc.), such as the following:

TABLE 2 Formu- lation Approximate Weight Percentages No. Cr B Fe Si C TiNi 1 10. 2.7 2.5 2.5 0.15 1.0 Balance 2 10. 3.0 2.5 2.5 0.15 2.0 Balance3 10. 4.8 2.5 2.5 0.15 10. Balance 4 17. 3.5 4.2 4.0 1.0 1.0 Balance 517. 3.5 4.5 4.0 1.0 2.0 Balance Note that while formulations 2, 3, and 5are particularly constituted to form a TiB phase, some TiB will form inall formulations because these reactions are typically not run toequilibrium.

Alternative compositions are as follows:

TABLE 3 Formu- lation Approximate Weight Percentages No. Cr B Fe Si CTiB₂ Ti Ni 6 10. 3.4 2.5 2.5 0.15 1.0 1.0 Bal. 7 10. 4.4 2.5 2.5 0.152.0 2.0 Bal. 8 10. 9.4 2.5 2.5 0.15 10. 10. Bal.

Further alternative compositions are as follows:

TABLE 4 Formu- Approximate Weight Percentages lation WC-12% No. Ni Cr FeSi B C Ti Co 9 33. 9.0 3.5 2.0 2.2 0.50 1.0 Bal. 10 33. 9.0 3.5 2.0 2.50.50 2.0 Bal.

Further alternative compositions are as follows:

TABLE 5 Formu- Approximate Weight Percentages lation WC-12% No. Ni Cr FeSi B C TiB₂ Ti Co 11 33. 9.0 3.5 2.0 2.9 0.50 1.0 1.0 Bal. 12 33. 9.03.5 2.0 3.9 0.50 2.0 2.0 Bal.

The columns labeled WC—12% Co in Tables 4 and 5 refer to a matrix oftungsten carbide (WC) and cobalt (Co) where a 12 wt. % of the matrix iscobalt. The matrix is formed not as an aggregate but rather as acomposite structure in which the tungsten carbide particles are “wetted”and “bonded” to form an integrated structure.

Boride-containing Ni-based reinforced materials are primarily composedof Ni, Cr, B, Si, and C, typically with Ti or TiB₂ which prompts theformation of TiB needles. The B content typically ranges from 1.5 to3.5% without any Ti or TiB₂. The addition of Ti and/or TiB₂ requiresadditional boron. Boron may be added at the ratio of 0.2% B per 1% Tiand 0.7% Ti per 1% TiB₂, depending on the Cr content, which is up toabout 16%. Higher Cr reinforced materials are generally formulated tocontain a large amount of B, which forms very hard chromium borides(˜1800 DPH).

These reinforced materials are microstructurally complex compared toconventional hard-facing protective layers. Ti, Ni, Cr, B, and Cdetermine the hardness and type of reinforced material within thestructure upon solidification, where B is the primary hard phase formingelement for which Ti, Ni, and Cr compete, and C is the second hard phaseformer. The dominant hard phase for the boride-containing Ni-basedreinforced materials are Ni₃B, CrB, Cr₅B₃, TiB₂, TiB and complexcarbides, M₂₃C₆ & M₇C₃ types. The addition of TiB₂ in the presence ofexcess titanium supplies boron for the formation of TiB.

As previously indicated, one purpose of Si is, in conjunction with B, toprovide self-fluxing characteristics. But Si is also an important matrixelement as a potential promoter of intermetallic precipitates, andconsequently Si typically has a major enhancing influence on the wearproperties of the reinforced materials. B content influences the levelof Si required for silicide (Ni₃Si) formation. The higher the B content,the lower the Si content that is required to form silicides.

Boride and carbide dispersions within the microstructure lead toexcellent abrasion resistance, with low stress abrasion resistancegenerally increasing with B and C contents. Boride-containing Ni-basedinterjoined materials possess moderate resistance to galling but aregenerally the least resistant to corrosion of the reinforced materials,due to the lack of Cr in the matrix that follows boride and carbideformation.

In some instances, the adhesion of a reinforced material to a substratemay be enhanced by partially melting the substrate surface to enhancethe formation of a reinforced material. For example, the diffusion ofmaterials between a substrate and precursor materials may be enhanced bysuch melting. Other modifications or enhancements that are enhanced withthis method include sintering, alloying and precipitation. Theseprocessing techniques may, in turn, be further employed to fuse orharden a reinforced material, or to enhance interjoining of a precursormaterial and the substrate, or to modify the resultant reinforcedmaterial composition or microstructural features in order to achievespecific mechanical, chemical, or electrical properties.

One example of a process where melting the surface of a substrate isbeneficial involves the application of boride-containing Ni-basedprecursor materials developed from brazing alloy compositions to asubstrate in a spray and fuse process. Parts (as substrates) may beprepared and coated as in typical thermal spray processes, and theprecursor materials may then be interjoined with the substrate by usingflame or torch methods, or by using an induction furnace, or by using avacuum, inert, or hydrogen furnace. During the fusing process, it isbelieved that oxides within the sprayed coating combine with some of theSi and B to form a borosilicate slag which floats to the surface of thedeposit. These Boride-containing Ni-based precursor materials generallyfuse between 1010-1175° C., which limits the substrate materials tosubstrates that can withstand this temperature range, or substrates thatcan be cooled to prevent substantial melting during processing.

As demonstration of a method for cooling a substrate, aluminum alloysubstrates were thermal spray coated with aluminum powder. The substratewas placed on a water-cooled backing plate. The samples wereunidirectionally heated in an IR furnace to heat the surface coating andfuse together any pores that formed in the aluminum coating. The IRradiation heated the aluminum coating and the surface of the substrateto a temperature of 950° C. for 60 seconds. Although the aluminumsubstrate had a melting temperature of 660° C., in this demonstrationthe process of heating the coating and the substrate to 950° C. did notmelt the substrate because of the cooling effect of the backing plate.

Methods described herein have been successfully tested on a variety ofcoatings which, historically, have proven difficult to apply. Forexample, the methods may be used to uniformly flux and sinter powdercoatings over entire surface areas at a time, effectively eliminatingresidual coating porosity without heating the underlying substrate tothe sintering temperature. Although other methods than those describedherein have been used to sinter an entire coating surface at the sametime without heating the underlying substrate, they typically produceinconsistent results (e.g., non-uniform sintering) over the treatedarea. Non-uniform sintering is further exacerbated when irregularsurface geometries are being treated. In contrast, the methods describedherein may be useful for effectively sintering powder coatings acrosssubstrate surfaces having complex geometries.

FIG. 6A depicts an electric arc welding rod 50. The welding rod 50 has ametal electrode 52 and a flux 54 is disposed adjacent a portion of theelectrode 52. A precursor material 56 is disposed adjacent a portion ofthe flux 54. In some embodiments the precursor material 56 may bepre-formed, such as a powder or glaze that is applied as a step in themanufacture of the welding rod 50. In alternate embodiments theprecursor material 56 may be formed in operation, such as by a powder ora glaze that is applied in the field prior to use of the welding rod 50.FIG. 6B depicts another embodiment of an electric arc welding rod,welding rod 60. The welding rod 60 has an electrode 62 and a precursormaterial 66 is disposed adjacent a portion of the electrode 62. A flux64 is disposed adjacent a portion of the precursor material. FIG. 6Cdepicts a further embodiment of an electric arc welding rod, welding rod70. Welding rod 70 has a metal electrode 72 and a coating 74 is disposedadjacent a portion of the electrode 72. The coating 74 includes aprecursor material and in some embodiments may also include a flux. Inembodiments where the coating 74 does not include a flux, the weldingrod 70 is typically used in an application that provides a protectiveatmosphere.

In some welding rod embodiments the metal electrode (e.g., 52, 62, or 72in FIGS. 6A, 6B, and 6C respectively) may be a stiff wire for use inwhat are commonly called “stick welders.” In other embodiments the metalelectrode may be a flexible wire for use in what are commonly called“wire-feed welders.” In some embodiments the precursor material (e.g.,56, 66, or portions of coating 74 in FIGS. 6A, 6B, and 6C, respectively)comprises titanium diboride and in some embodiments the precursormaterial comprises titanium monoboride and in some embodiments theprecursor material comprises both titanium monoboride and titaniumdiboride. In some embodiments the precursor material further comprises aβ-titanium stabilizer. In some embodiments the precursor materialincludes titanium metal as a source of available titanium to assist inthe formation of a composite structure.

An embodiment of a material for use in forming a composite structure isprovided. The material may be in the form of solids (such as a bar, rodor wire), particulates (such as powders or flakes), or a glaze. Thematerial typically comprises a precursor material and a flux. In someembodiments the precursor material comprises titanium diboride and insome embodiments the precursor material comprises titanium monoborideand in some embodiments the precursor material comprises both titaniummonoboride and titanium diboride. In some embodiments the precursormaterial further comprises a β-titanium stabilizer. In some embodimentsthe precursor material includes titanium metal as a source of availabletitanium to assist in the formation of a composite structure.

Localized heating sources may be used for original equipmentmanufacturing of cutting and grinding tools and other articles ofmanufacture that are subject to severe surface erosion in service. Forexample, FIG. 7A illustrates a composite structure grinder 80 having asubstrate 82. Reinforced material 84 that is configured as lines 86 isinterjoined with the substrate 82 to provide the composite structuregrinder 80. The width of the lines 86 and the spacing between the lines86 is typically between approximately one half and oneone-hundred-thousandths of the largest physical dimension of thesubstrate. The reinforced material 84 may be made by disposing precursormaterials on the substrate 82 and using a localized heating source suchas a scanning laser to heat the precursor material and at least aportion of the substrate 82 in the presence of an oxidation preventativeuntil at least a portion of the precursor material forms a reinforcedmaterial 84 as lines 86 interjoined with the substrate 82 to provide thecomposite structure grinder 80.

FIG. 7B illustrates a composite structure grinder 90 having a substrate92. Reinforced material 94 configured as spots 96 is interjoined withthe substrate 92 to provide the composite structure grinder 90. Thewidth of the spots 96 and the spacing between the spots 96 is typicallybetween approximately one half and one one-hundred-thousandths of thelargest physical dimension of the substrate 92. The reinforced material94 may be made by disposing precursor materials on the substrate 92 andusing a localized heating source such as a scanning laser to heat theprecursor material and at least a portion of the substrate 92 in thepresence of an oxidation preventative until at least a portion of theprecursor material forms a reinforced material 94 as spots 96interjoined with the substrate 92 to provide the composite structuregrinder 90.

Localized heating sources may also be used for making compositematerials in non-factory environments such as repair shops and fieldmaintenance facilities. For example the cutting edges of heavyexcavation and mining machinery are subject to harsh environments thatmay rapidly erode the cutting surfaces. Localized heating sources may beemployed with embodiments described herein to rebuild such cuttingsurfaces with very hard composite materials.

EXAMPLES

A series of tests were conducted to produce and examine variousreinforced materials formed on two substrate materials. The reinforcedmaterials were produced by disposing precursor materials on thesubstrates and then using a tungsten-inert-gas (TIG) welder with argonas the cover gas to provide heat to melt the precursor materials. FIG.8A illustrates the layout of a specific test array 100. A titaniumsubstrate 102 was segmented into eight numbered regions (labeled 1through 8). The combinations of precursor materials that were disposedon the substrate in each of the regions are identified by labeled “row”and “column” headings. For example, region 1 had no precursor materialand no flux, and it served as a control specimen. Region 2 had boron(with no flux) as a precursor material; region 3 had TiB₂ (with no flux)as the precursor material, and so forth, with region 8 having a mixtureof CrB₂ and a boric acid flux as the precursor material. To heat theprecursor materials for one type of test, the TIG welder was passedacross the test array in two transverse lines 104 and 106. In a secondtype of test the TIG welder also positioned over a series of spots 108,one spot in each of the eight numbered regions. In each of these teststhe residence time of the TIG welder at each heated location was ofsufficient duration to visually observe that the precursor materialsmelted under the TIG welder.

FIG. 8B illustrates the layout of a second test array 110. A mild steelsubstrate 112 was segmented into four numbered regions (labeled 9through 12). The combinations of precursor materials that were disposedon the substrate in each of the regions are identified by labeled “row”and “column” headings. The TIG welder was passed across the test arrayin two transverse lines 114 and 116 and the TIG welder was alsopositioned over a series of spots 118, one spot in each of the fournumbered regions. FIG. 8C illustrates the layout of a third test array120 using a titanium substrate 122. The TIG welder was passed across thetest array in three transverse lines 124, 126, and 128. A mixture ofboron and boric acid flux was disposed as precursor material on thesubstrate 122. The transverse line 124 of the TIG welder was made at apower level of 75 amps, the transverse line 126 was made at a powerlevel of 50 amps, and the transverse line 128 was made at a power levelof 25 amps.

FIG. 9 is a 50× magnification photomicrograph of a cross section ofmaterial taken from the transverse line 104 portion region 1 (asidentified in FIG. 8A) of test array 100. Region 1 is an area where noprecursor material was applied, so no reinforced material was createdinterjoined with the titanium substrate 102 and no composite structurewas formed. Illustrated in FIG. 9 are hardness test probe marks 150,which are also shown in FIGS. 10-15, 19-22, and 25-27.

FIGS. 10-12 are 50× magnification photomicrographs of reinforcedmaterials 162, 172A, B, and C and 182 interjoined with the titaniumsubstrate 102 of FIG. 8A to form composite structures 164, 174 and 184respectively. These photomicrographs are cross sections of materialtaken from the transverse line 104 portions of regions 2, 3, and 4(respectively) of test array 100. Note that in FIG. 11, three separateforms of reinforced material (172A, 172B, and 172C) are evident.

FIG. 13 is a 50× magnification photomicrograph of a cross section ofmaterial taken from the transverse line 106 portion of region 5 (asidentified in FIG. 8A) of test array 100. Region 5 is an area where aboric acid flux was applied. In addition to being a flux, the boric acidwas a “precursor material” (as the term is used herein) because theboron in the flux formed reinforced material 192 that was interjoinedwith the titanium substrate 102 to form a composite structure 194. FIGS.14-16 are 50× magnification photomicrographs of reinforced materials202, 212 and 222 interjoined with the titanium substrate 102 of FIG. 8Ato form composite structures 204, 214 and 224, respectively. FIGS. 14and 16 are cross sections of material taken from the transverse line 106portions of regions 6 and 8 (respectively) of test array 100. FIG. 15 isa cross section of material taken from the spot 108 portion of region 7of test array 100.

FIG. 17 is a plot of Vickers hardness measurements taken at crosssections sampled from the spots associated with regions 1-8 of FIG. 8A,at various depths below the exposed surface of reinforced materialsformed at those spots (or at various depths below the exposed surface ofthe substrate in the case of spot portion of region 1). The hardnessnear the surface of the reinforced materials is higher than the harnessof the substrate near its surface where (again, as illustrated by thespot portion of region 1) reinforced material was not formed adjacentthe surface of the substrate.

FIG. 18 is a plot of Vickers hardness measurements taken at crosssections sampled from the transverse lines 104 and 106 associated withregions 1-8 of FIG. 8A. The hardness near the surface of the reinforcedmaterials is higher than the hardness of the substrate near its surfacewhere (as illustrated by curve 1 taken from transverse line 104 inregion 1) reinforced material was not formed adjacent the surface of thesubstrate.

FIGS. 19-22 are 50× magnification photomicrographs of reinforcedmaterials 232, 242, 252 and 262 interjoined with the mild steelsubstrate 112 to form composite structures 234, 244, 254 and 264respectively. FIGS. 19 and 20 are cross sections of material taken fromthe transverse line 114 portions of regions 9 and 10 (respectively) oftest array 110 shown in FIG. 8B. FIG. 21 is a cross section of materialtaken from the spot portion of region 11 of test array 110. FIG. 22 is across section of material taken from the transverse line 116 portion ofregion 12 of test array 110 shown in FIG. 8B.

FIG. 23 is a plot of Vickers hardness measurements taken at crosssections sampled from the spots associated with regions 9-12 of FIG. 8B,at various depths below the exposed surface of reinforced materialsformed at those spots. FIG. 24 is a plot of Vickers hardnessmeasurements taken at cross sections sampled from the transverse lines114 and 116 associated with regions 9-12 of FIG. 8B. The hardness nearthe surface of the reinforced materials is higher than the hardness ofthe substrate.

FIG. 25 is a 50× magnification photomicrograph of a composite structure274 formed on the titanium substrate 122 where boron and boric acid fluxwere the precursor materials and heat was provided by a TIG welder at 75amps (transverse line 124 on FIG. 8C). FIG. 26 is a 50× magnificationphotomicrograph of a composite structure 284 formed on the titaniumsubstrate 122 where boron and boric acid flux were the precursormaterials and heat was provided by a TIG welder at 50 amps (transverseline 126 on FIG. 8C). FIG. 27 is a 50× magnification photomicrograph ofa composite structure 294 formed on the titanium substrate 122 whereboron and boric acid flux were the precursor materials and heat wasprovided by a TIG welder at 25 amps (transverse line 128 on FIG. 8C). Inthe photomicrographs of FIGS. 25-27 there are no obvious lines ofdemarcation between reinforced material and substrate material.

FIG. 28 is a plot of Vickers hardness measurements taken from crosssections of FIGS. 25, 26 and 27, which where sampled from the transverselines 124 (75 Amps), 126 (50 Amps) and 128 (25 Amps) depicted in FIG.8C.

In summary, embodiments disclosed herein provide composite structuresthat include a reinforced material interjoined with a substrate andmethods of forming a reinforced material interjoined with a surface of asubstrate to form a composite structure. The foregoing descriptions ofembodiments of the disclosure have been presented for purposes ofillustration and exposition. They are not intended to be exhaustive orto limit the disclosed embodiments to the precise forms disclosed.Obvious modifications or variations are possible in light of the aboveteachings. The embodiments are chosen and described in an effort toprovide the best illustrations of the principles of the disclosedembodiments and its practical application, and to thereby enable one ofordinary skill in the art to utilize the various embodiments and withvarious modifications as are suited to the particular use contemplated.All such modifications and variations are within the scope of thedisclosure as determined by the appended claims when interpreted inaccordance with the breadth to which they are fairly, legally, andequitably entitled.

1. A composite structure comprising a reinforced material intermingled with a substrate, wherein the reinforced material comprises a compound selected from the group consisting of titanium monoboride, titanium diboride, and combinations thereof disposed at least partially below a surface of the substrate.
 2. The composite structure of claim 1 wherein the reinforced material comprises titanium monoboride.
 3. The composite structure of claim 1 wherein the reinforced material comprises structures selected from the group consisting of β-titanium, TiB needles, TiB pillars, and combinations of two or more of the three.
 4. The composite structure of claim 1 wherein the composite structure comprises reinforced material intermingled with the substrate in a structure selected from the group consisting of a line, a spot, and a combination thereof.
 5. The composite structure of claim 1 wherein the substrate comprises aluminum.
 6. The composite structure of claim 1 wherein the substrate consists of aluminum or an aluminum alloy.
 7. The composite structure of claim 1 wherein the reinforced material extends into the substrate to a depth of approximately five microns or less.
 8. The composite structure of claim 1 wherein the reinforced material includes a plurality of high aspect ratio particles of titanium monoboride, each high aspect ratio particle having at least three dimensions wherein one dimension is approximately five times longer than either of the other two dimensions. 